This invention relates to a coating composition containing certain ungelled urethane modified alkyd resins and a process for coating a substrate with the coating composition. Also disclosed are certain ungelled urethane modified alkyd resins.
Due to the high cost of imported energy and petroleum based raw materials as well as increased environmental awareness, the coatings industry has been attempting to lower the volatile organic content of its paints. This has forced a shift to higher solids coating systems. In order to reach the required goals while maintaining desirable application properties, it has been necessary to lower the viscosity of the vehicle system. This generally requires a concomitant reduction in the molecular weight of the major polymers of the composition. The industry has faced considerable difficulty with air drying alkyd resins in this regard. Lower molecular weight materials generally do not develop the same hardness and through-dry in thick films in the same amount of time compared to materials having a higher molecular weight. The present invention directs itself towards the production of materials which when oxidatively cured, develop properties comparable to, or better than, conventional lower solids systems.